This invention generally relates to pneumatic ratchet drive wrenches and more particularly to a pneumatic ratchet drive wrench having a single spring for both biasing a pawl into engagement with an output member and inhibiting counter-rotation of the output member.
The invention is especially concerned with a powered wrench that rotates an output member with a socket for turning a fastener element such as a bolt or a nut. Wrenches of this type are useful in automotive repair and industrial applications. Conventionally, pneumatic ratchet drive wrenches comprise an air motor for powering the wrench, an internal ratchet mechanism for transferring motion of the motor and an output member for transmitting such motion to a workpiece. Put simply, the internal ratchet mechanism typically includes a rotating offset shaft spinning with the air motor that in turn pivots a rocker having pawls attached which repeatedly engage a set of teeth on the output member, causing the member to rotate in a desired direction. During each rotation of the air motor, the output member is rotated a fraction of a revolution. By repeatedly engaging the output member and rotating it only a short distance, great mechanical advantage is obtained and the high-speed rotation of the air motor is readily converted to a high-torque, yet more slowly rotating, output member. These advantages are well understood in the relevant art.
Despite the simplicity of the concept behind a pneumatic ratchet drive wrench, the internal ratchet mechanisms of conventional pneumatic ratchet drive wrenches are complex and require many parts interacting with one another. For instance, wrenches traditionally require complex mechanisms for ensuring that the output member of the wrench does not rotate counter the desired direction during wrench use. These mechanisms often include multiple parts that serve the limited purpose of inhibiting counter-rotation of the output member. Similarly, size and space limitations of the wrench often compel the fashioning of elaborate, interactive components. For example, a reverse lever must often be incorporated directly with a drive link of the wrench, requiring a larger and heavier drive link than required for performing the drive link function alone (e.g., U.S. Pat. No. 5,535,646). Simplification of such a wrench by eliminating redundant parts and reducing the size and complexity of required parts improves overall wrench design.
It is an aim of wrench manufacturers to provide a pneumatic ratchet drive wrench that uses energy efficiently and incorporates fewer and simpler components. One difficulty in the fashioning of such a wrench is providing an output member that may rotate in both directions, yet will not rotate opposite the desired direction between subsequent pawl engagements. Typically, wrenches include anvil pressure washers for impeding counter-rotation of the output member. Other configurations incorporate stop mechanisms of increased complexity and cost. It is therefore the aim of the present invention to provide a stop mechanism that is inexpensive to manufacture and simple to incorporate into another spring of the invention. It is also the aim of the present invention to provide a wrench that manages wear more efficiently by decreasing wear of expensive or difficult to replace components, while transferring the wear to more easily replaceable and inexpensive components.
Among the several objects and features of the present invention may be noted the provision of a pneumatic ratchet drive wrench which reduces the number and complexity of wrench components; the provision of such a wrench which decreases the wear exhibited on expensive or difficult to replace components; the provision of such a wrench which allows for a smaller overall wrench size for access into small spaces; the provision of such a wrench which allows for more relaxed tolerances for wrench components; and the provision of such a wrench which may be manufactured inexpensively.
Generally, a pneumatic ratchet drive wrench of the present invention comprises a housing. An air inlet is supported by the housing. The inlet is sized and shaped for connection to a source of pressurized air. An air motor is disposed in the housing and is in fluid communication with the air inlet for receiving pressurized air. The motor includes a rotatable drive shaft that rotates when pressurized air passes through the motor. A rocker is disposed pivotably within the housing and is operatively connected to the drive shaft so that rotation of the drive shaft induces oscillation of the rocker. At least one pawl is pivotably attached to the rocker. An output member has teeth and is mounted in the housing for rotation about its longitudinal axis. The output member projects from the housing for transmitting torque to an object. The at least one pawl is shaped and sized for engagement with the output member teeth to turn the output member. At least one spring is supported in the housing for biasing the at least one pawl against the teeth. The at least one spring is shaped and sized for restraining the output member from rotation opposite the rotation induced by the pawl.
In another aspect of the present invention, a pneumatic ratchet drive wrench comprises a housing, an air inlet, an air motor and a rocker generally as set forth above. The wrench further comprises at least two pawls pivotably attached to the rocker and an output member having teeth. The output member is mounted in the housing for rotation about its longitudinal axis and projects from the housing for transmitting torque to an object. The pawls are shaped and sized for alternate engagement with the output member teeth to turn the output member. At least one spring is supported in the housing for biasing at least one of the at least two pawls against the teeth. The at least one spring is shaped and sized for restraining the output member from rotation opposite the rotation induced by the at least one pawl. The spring includes a pawl-engaging portion, engaging the pawl and biasing the pawl against the teeth, a stop portion, engagable with the teeth to restrain the output member from rotation in a direction opposite that induced by the pawi, and a coil portion, formed to independently bias the pawl-engaging portion and the stop portion. The coil portion comprises a pawl coil for biasing the pawl-engaging portion and a stop coil for biasing the stop portion. The stop portion and teeth are shaped and arranged in the housing so that upon rotation of the output member in the direction induced by the pawl, the teeth push the stop portion outwardly from the output member to permit rotation. Upon rotation of the output member in the opposite direction, the stop portion engages the teeth to block the opposite rotation.
Other objects and features will be in part apparent and in part pointed out hereinafter.